Apoptosis In Adult Cardiac Myocytes Research Articles

Osteopontin stimulates apoptosis in adult cardiac myocytes via the involvement of CD44 receptors, mitochondrial death pathway, and endoplasmic reticulum stress

Increased osteopontin (OPN) expression associates with increased myocyte apoptosis and myocardial dysfunction. The objective of this study was to identify the receptor for OPN and get insight into the mechanism by which OPN induces cardiac myocyte apoptosis. Adult rat ventricular myocytes (ARVMs) and transgenic mice expressing OPN in a myocyte-specific manner were used for in vitro and in vivo studies. Treatment with purified OPN (20 nM) protein or adenoviral-mediated OPN expression induced apoptosis in ARVMs. OPN co-immunoprecipitated with CD44 receptors, not with β1 or β3 integrins. Proximity ligation assay confirmed interaction of OPN with CD44 receptors. Neutralizing anti-CD44 antibodies inhibited OPN-stimulated apoptosis. OPN activated JNKs and increased expression of Bax and levels of cytosolic cytochrome c, suggesting involvement of mitochondrial death pathway. OPN increased endoplasmic reticulum (ER) stress, as evidenced by increased expression of Gadd153 and activation of caspase-12. Inhibition of JNKs using SP600125 or ER stress using salubrinal or caspase-12 inhibitor significantly reduced OPN-stimulated apoptosis. Expression of OPN in adult mouse heart in myocyte-specific manner associated with decreased left ventricular function and increased myocyte apoptosis. In the heart, OPN expression increased JNKs and caspase-12 activities, and expression of Bax and Gadd153. Thus, OPN, acting via CD44 receptors, induces apoptosis in myocytes via the involvement of mitochondrial death pathway and ER stress.

Exogenous ubiquitin modulates chronic β-adrenergic receptor-stimulated myocardial remodeling: role in Akt activity and matrix metalloproteinase expression

β-Adrenergic receptor (β-AR) stimulation increases extracellular ubiquitin (UB) levels, and extracellular UB inhibits β-AR-stimulated apoptosis in adult cardiac myocytes. This study investigates the role of exogenous UB in chronic β-AR-stimulated myocardial remodeling. l-Isoproterenol (ISO; 400 μg·kg(-1)·h(-1)) was infused in mice in the presence or absence of UB (1 μg·g(-1)·h(-1)). Left ventricular (LV) structural and functional remodeling was studied 7 days after infusion. UB infusion enhanced serum UB levels. In most parts, UB alone had no effect on morphometric or functional parameters. Heart weight-to-body weight ratios were increased to a similar extent in the ISO and UB + ISO groups. Echocardiographic analyses showed increased percent fractional shortening, ejection fraction, and LV circumferential stress and fiber-shortening velocity in the ISO group. These parameters were significantly lower in UB + ISO vs. ISO. Isovolumic contraction and relaxation times and ejection time were significantly lower in ISO vs. UB + ISO. The increase in the number of TUNEL-positive myocytes and fibrosis was significantly higher in ISO vs. UB + ISO. Activation of Akt was higher, whereas activation of GSK-3β and JNKs was lower in UB + ISO vs ISO. Expression of MMP-2, MMP-9, and TIMP-2 was higher in UB + ISO vs ISO. In isolated cardiac fibroblasts, UB enhanced expression of MMP-2 and TIMP-2 in the presence of ISO. Neutralizing UB antibodies negated the effects of UB on MMP-2 expression, whereas recombinant UB enhanced MMP-2 expression. UB activated Akt, and inhibition of Akt inhibited UB + ISO-mediated increases in MMP-2 expression. Thus, exogenous UB plays an important role in β-AR-stimulated myocardial remodeling with effects on LV function, fibrosis, and myocyte apoptosis.

β-Adrenergic receptor-stimulated apoptosis in adult cardiac myocytes involves MMP-2-mediated disruption of β1 integrin signaling and mitochondrial pathway

Stimulation of beta-adrenergic receptors (beta-AR) induces apoptosis in adult rat ventricular myocytes (ARVMs) via the JNK-dependent activation of mitochondrial death pathway. Recently, we have shown that inhibition of matrix metalloproteinase-2 (MMP-2) inhibits beta-AR-stimulated apoptosis and that the apoptotic effects of MMP-2 are possibly mediated via its interaction with beta1 integrins. Herein we tested the hypothesis that MMP-2 impairs beta1 integrin-mediated survival signals, such as activation of focal adhesion kinase (FAK), and activates the JNK-dependent mitochondrial death pathway. Inhibition of MMP-2 using SB3CT, a selective gelatinase inhibitor, significantly increased FAK phosphorylation (Tyr-397 and Tyr-576). TIMP-2, tissue inhibitor of MMP-2, produced a similar increase in FAK phosphorylation, whereas treatment of ARVMs with purified active MMP-2 significantly inhibited FAK phosphorylation. Inhibition of MMP-2 using SB3CT inhibited beta-AR-stimulated activation of JNKs and levels of cytosolic cytochrome c. Treatment of ARVMs with purified MMP-2 increased cytosolic cytochrome c release. Furthermore, inhibition of MMP-2 using SB3CT and TIMP-2 attenuated beta-AR-stimulated decreases in mitochondrial membrane potential. Overexpression of beta1 integrins using adenoviruses expressing the human beta1A-integrin decreased beta-AR-stimulated cytochrome c release and apoptosis. Overexpression of beta1 integrins also inhibited apoptosis induced by purified active MMP-2. These data suggest that MMP-2 interferes with the beta1 integrin survival signals and activates JNK-dependent mitochondrial death pathway leading to apoptosis.

Intracellular Ca 2+ fluctuation through multiple Ca 2+ regulatory proteins is inevitable for initiating apoptosis in adult cardiac myocytes

Adult cardiac myocytes show a dynamic and unique process during execution of apoptosis; they exhibit beating just before and at the early phase of apoptosis (Am J Pathol. 2001), suggesting important roles of intracellular Ca 2+ concentration ([Ca 2+]i) and Ca 2+ regulatory proteins for initiating apoptosis in those cells. In the present study, we examined the regulatory mechanisms of Ca 2+ regulatory proteins for initiating apoptosis in adult cardiac myocytes, which was induced by activation of β-adrenergic receptor by isoproterenol (10 −5 M). Apoptosis was evident, as documented by activated caspase-3, DNA fragmentation based on in situ nick end-labeling (TUNEL) and DNA ladder pattern, and apoptotic ultrastructure. These apoptotic features were found significantly inhibited by L-type Ca 2+ channel antagonist (nifedipine), SERCA antagonist (thapsigargin), and ryanodine receptor antagonist (ryanodine) in a dose-dependent manner. According to serial observation under a real-time videomicroscope, those antagonists inhibited not only apoptotic morphological change but also the pre-apoptotic beating. These findings suggest an important role of a fluctuation of [Ca 2+]i - i.e., not only an increase in [Ca 2+]i through L-type Ca 2+ channel or ryanodine receptor but also a decrease in it through SERCA, for initiating cardiac myocyte apoptosis, implying an exquisite regulation of initiating apoptosis in adult cardiac myocytes by multiple Ca 2+regulatory proteins.

O2-07 HAX-1 blocks apoptosis in adult cardiac myocytes through inhibition of caspase-9

O2-07 HAX-1 blocks apoptosis in adult cardiac myocytes through inhibition of caspase-9

Mechanisms of thromboxane A2associated apoptosis in adult cardiac myocytes: role of protein kinase C zeta mediated downregulation of Akt activity

Mechanisms of thromboxane A2associated apoptosis in adult cardiac myocytes: role of protein kinase C zeta mediated downregulation of Akt activity

Protein kinase C-zeta modulates thromboxane A(2)-mediated apoptosis in adult ventricular myocytes via Akt.

We hypothesized that thromboxane A(2) (TxA(2)) receptor stimulation directly induces apoptosis in adult cardiac myocytes. To investigate this, we exposed cultured adult rat ventricular myocytes (ARVM) to a TxA(2) mimetic [1S-[1alpha,2alpha(Z),3beta(1E,3S*),4alpha]]-7-[3-[3-hydroxy-4-(4-iodophenoxy)-1-butenyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid (I-BOP) for 24 h. Stimulation with I-BOP induced apoptosis in a dose-dependent manner and was completely prevented by a TxA(2) receptor antagonist, SQ-29548. We further investigated the role of protein kinase C (PKC) in this process. TxA(2) stimulation resulted in membrane translocation of PKC-zeta but not PKC-alpha, -betaII, -delta, and -epsilon at 3 min and 1 h. The activation of PKC-zeta by I-BOP was confirmed using an immune complex kinase assay. Treatment of ARVM with a cell-permeable PKC-zeta pseudosubstrate peptide (zeta-PS) significantly attenuated apoptosis by I-BOP. In addition, I-BOP treatment decreased baseline Akt activity and its decrease was reversed by treatment with zeta-PS. The inhibition of phosphatidylinositol 3-kinase upstream of Akt by wortmannin or LY-294002 abolished the antiapoptotic effect of zeta-PS. Therefore, our results suggest that the activation of PKC-zeta modulates TxA(2) receptor-mediated apoptosis at least, in part, through Akt activity in adult cardiac myocytes.